Why must a plain water stream extinguisher never be used on energized electrical equipment?
- The stream can carry current back to the operator
- Water makes the insulation burn faster
- The stream breaks into hydrogen and oxygen
- Water lowers the voltage and damages the equipment
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A. The stream can carry current back to the operator
Ordinary water conducts electricity, so a solid stream gives the current a path to the person holding the extinguisher. That is why plain water units carry only a Class A rating.
Reference: NFPA 10: extinguisher types and agents
The power to a burning electric motor is shut off and locked out. How should the fire now be treated?
- As a Class C fire until the motor has cooled to room temperature
- As a Class A or B fire, depending on what is burning
- As a Class D fire because metal parts are hot
- As a Class K fire if lubricating oil is involved
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B. As a Class A or B fire, depending on what is burning
Class C exists only because of the shock hazard. Once the equipment is de-energized the fire is whatever the burning material is, usually Class A insulation or Class B oil. It does not stay Class C just because the equipment is electrical.
Reference: NFPA 10: classification and rating of fires and extinguishers
What is the main difference between an inspection and maintenance of an extinguisher?
- Inspection is done by the fire marshal; maintenance is done by the building owner
- Inspection is a quick visual check; maintenance is a thorough examination
- Inspection includes discharging the unit; maintenance does not
- Inspection is done on the bench; maintenance is done on the wall
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B. Inspection is a quick visual check; maintenance is a thorough examination
An inspection confirms the unit is where it belongs, visible, accessible and apparently charged and undamaged. Maintenance examines the mechanical parts, agent and expelling means and corrects problems.
Reference: NFPA 10: inspection, maintenance and recharging
What does pre-engineered mean for a kitchen suppression system?
- It is custom calculated by an engineer for each kitchen
- It is assembled at the factory and cannot be altered
- It is designed by the local fire marshal's office
- It is installed within the limits of its listed manual
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D. It is installed within the limits of its listed manual
Nozzle types, pipe lengths, flow points and appliance coverage were all fire tested, and the installer must stay inside those listed limits. No hydraulic calculation is done, but the limits cannot be exceeded.
Reference: NFPA 17A and NFPA 96: wet chemical systems for commercial cooking
After the cartridge is punctured on a cartridge-operated extinguisher, how is the discharge controlled?
- By squeezing a lever on top of the valve on the agent shell
- By turning the cartridge to open or close it
- By tilting the shell forward or backward
- By squeezing the shutoff nozzle at the end of the hose
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D. By squeezing the shutoff nozzle at the end of the hose
The cartridge charges the shell and hose, and the operator starts and stops the flow at the hose nozzle. There is no squeeze-grip valve on the shell as there is on a stored-pressure unit.
Reference: NFPA 10: extinguisher types and operation